Process for producing white mechanical wood pulp from pine wood



Patented Apr. 29, 1941 ,ipu

PROCESS FOR PRdDUCING WHITE MECHAN- IOAL WOOD PULP FROM PINE WOOD Otto Primavesi, Berlin-Tempelhof, Germany No Drawing.

Application March 22, 1938, Serial No. 197,503. In Germany April 28, 193'? 3 Claims.

It is known that the higher resin-fatty acid content of pine as compared with that of fir or spruce, and the likewise greater amounts of glycides and lignins present renders dimcult a preparation of pine wood in the form of white mechanical wood pulp since the resins or the like lead to a fouling of the sieve or wire, felt and cylinder of the paper machine. It is true that these difficulties due to resin have already been successfully removed by steaming the pine wood before the grinding, but one had to put up with the fact that the wood or the mechanical wood pulp became brown as a result and, as so-called brown mechanical wood pulp, could be used only for special purposes.

Efiorts have not been lacking therefor to work up the pine wood to white mechanical wood pulp with avoidance of these resin difliculties, but all efforts in this respect up to now have met with only a limited success. The essential feature of all previous efiorts in this direction consisted in saponifying or dissolving the resin-fatty acids arising. This was simply attained by adding suitable quantities of caustic soda, soda solution or resin solvents during the grinding. This process however is only of limited application since too strong enrichment oi the stud suspension with resin soap or resin solution leads to such a nothing in the various sections oi the machine that the further working up of the same likewise involves great dificulties. ularly the case when the grinding operation is carrled out with circulating water.

it is also already mown to convert the resin acids oi the wood into lime soap instead of into soda soap, milk of lime being added to the grinding water. The lime soap formation itseli however involves considerable drawbacks since it likewise leads to an early fouling of the sieve and i'elt, for which reason also lime soap formation is very much feared in all washing processes.

The process forming the subject of this invention avoids these drawbacks by producing the dreaded lime soap during the grinding by addition of alkaline earth, preferably alkaline earth metal chloride, such as calcium chloride, but binding this soap, by an addition of alkali phosphate, for example trisodium phosphate, following thereon, to the alkaline earth metal phos- This is more partic-,

phate forming thereby and so making it harmless. In this way therefore fillers form which behave similarly to the usual fillers, such as kaolin, and consequently are deposited in the paper web without any further damage.

In order in every case to ensure the necessary stability of the lime soap bound for example to calcium phosphate and its formation itself, it is advisable when using alkaline earth metal salts to maintain the alkalinity of the grinding water by addition of alkali, such as soda or the like. If the mechanical wood pump is furthermore to be bleached, which as a rule is effected in an acid manner, for example with the aid of sulphurous acid, then it is advisable to add for example calcium chloride in excess, which after the bleaching then forms gypsum which behaves just like the above-mentioned fillers. In order to make the process still more eflicient it is further advisable first of all to dry the wood to be worked up, as known per se, since by this means more uniform working conditions are created.

I claim:

1. In the production of white mechanical wood pulp from pine wood, the process which comprises grinding pine wood in the presence of an aqueous solution of a calcium salt in amount sufiicient to form a calcium soap with the resin acids of the wood and adding a soluble alkali metal phosphate, thereby converting said calcium soap into calcium phosphate and. forming an inert, filler-like material which is unohjectionable in paper making processes.

2. In the production of white mechanical wood pulp from pine wood, the process which comprises grinding pine wood in the presence of an aqueous solution of calcium chloride in amount sufficient to form a calcium soap with the resin acids of the wood and adding sodium phosphate, thereby converting said calcium soap into calcium phosphate and forming an inert, filler-like material which is unobjectionable in paper making processes.

3. The process of claim 2 wherein an alkali is added to said aqueous solution in order to maintain an alkaline reaction during the grinding procedure.

OTTO PRIMAVESI. 

